Because mallards are so widespread, they often crossbreed with other duck species, including escaped domestic ducks. This hybridization can create unique plumage colours and indistinct markings that make identification difficult. Hybrid mallards may have a creamy buff or all over brown plumage, or may show splotches of white or black in unexpected places. They may also have odd tufts of feathers around the head, wings or tail.

Identifying hybrid mallards can be a challenge, but certain clues and pinpoint the bird's identity. On males, look for the distinct curled tail feathers, and look for plumage patterns similar to the coloured head bordered by a collar or the coloured speculum, even if the colours on the hybrid duck don't match classic mallard plumage. Another indication of the bird's species will be others in the flock – mallards are highly social and many flocks will have hybrid members.